1. Field of the Invention
The present invention relates generally to a system for minimizing the deleterious impact of oil-derived phosphorus containing compounds on automotive exhaust aftertreatment systems.
2. Background of the Invention
Automotive oils typically contain a zinc dialkyldithiophosphate (ZDDP) additive which forms an antiwear coating on engine components and acts as an antioxidant in the oil. Although engines are designed to minimize the quantity of engine oil exiting the engine via the combustion chamber and exhaust system, it is inevitable that a small fraction of engine oil is released by this mechanism. The ZDDP additive of engine oil deleteriously affects catalytic converters due to phosphorus from the ZDDP interfering with active sites within the catalyst. These phosphorus containing species deposit onto, or react with washcoat components, such as aluminum oxide and cerium oxide, and remain there indefinitely. This phenomenon is commonly referred to as phosphorus poisoning.
Measures to eliminate or reduce ZDDP in engine oils have been investigated. Alternatives to ZDDP have been produced which have been shown to provide antioxidant and antiwear properties similar to ZDDP. However, they are cost prohibitive. Engine oils may be formulated with a lesser amount of ZDDP with the consequences that engine wear and oil oxidation increase, the former limiting engine life and the latter reducing useful oil life.
The inventor of U.S. Pat. No. 5,857,326 has disclosed an exhaust poison trap which comprises a helical wall dividing the exhaust chamber into longitudinal helical passages for exhaust gas flow and porous means covering the interior of the peripheral wall. The inventor of ""326 teaches that exhaust gas is directed in a helical path causing particulate matter in the gas to be accelerated outwardly by centrifugal force and trapped in the porous means. The inventor of the present invention has recognized several limitations of the approach in ""326. The helical passages cause the exhaust gases to be rotated and particles that have a diameter less than a certain size follow the flow and avoid being trapped in the porous means near the walls of the tube and larger particles impact the porous means near the walls. The device disclosed in ""326 has the capability of causing only the largest particles to be removed. The figures in ""326 indicate that the helical wall causes the flow to rotate through at least two revolutions and as many as four revolutions. The length of the exhaust poison trap is approximately two to four pipe diameters long with the disadvantages of complicating the packaging of the exhaust poison trap and increasing the weight of the trap, the thermal mass of which interferes with the desire to bring the catalytic converter to its operating temperature as soon as possible after starting the engine to control cold start emissions.
Disadvantages of prior art are overcome by an exhaust aftertreatment system for a spark-ignition, reciprocating internal combustion engine having a catalytic converter in an exhaust duct of the engine which receives an exhaust gas stream from the engine. The system comprises a trap in the exhaust duct located upstream of the catalytic converter. The trap is made of a porous ceramic or metallic material having an average pore size greater than about 80 micrometers. The porous material substantially fills the cross-section of the exhaust duct and has a volume of than 10% of a swept volume of the engine""s cylinders coupled to the trap. Exhaust gases undergo multiple, random turns in traveling from an upstream side to a downstream side of the trap. The trap is located within 15 centimeters of the catalytic converter. An exhaust gas component sensor is placed downstream of the phosphorus trap.
Also disclosed is an exhaust aftertreatment system for processing exhaust gases from a reciprocating internal combustion engine, which includes a catalytic converter disposed in an exhaust duct of the engine. The catalytic converter has channels for conducting exhaust gases from an upstream end to a downstream end. The channels are substantially parallel to each other and parallel to a direction of flow through the catalytic converter. The catalytic converter has a ceramic or metallic porous material disposed within the channels from the upstream end of the catalytic converter for a predetermined distance along the catalytic converter. The porous material has randomly oriented passageways causing the exhaust gases to undergo multiple turns in the course of being transmitted through the porous material.
Also disclosed is an exhaust aftertreatment system for a reciprocating internal combustion engine comprising a phosphorus trap in an exhaust duct of the engine made of a porous material and substantially filling the cross-section of the exhaust duct. The porous material has an average pore size greater than a predetermined pore size and has randomly oriented passageways forcing exhaust gases passing through to undergo multiple turns. The system also has a catalytic converter disposed in the exhaust duct of the engine located downstream of the phosphorus trap and an electronic control unit operably connected to the engine. The electronic control unit provides an indication of an amount of phosphorous containing material trapped in the phosphorus trap and raises temperature in the phosphorous trap above a predetermined temperature when the amount of phosphorous containing material exceeds a predetermined quantity. The indication is based on time of operation or a value of an engine parameter since the predetermined temperature has been achieved.
A primary advantage of the present invention is that phosphorus contamination of the exhaust aftertreatment system can be decreased by approximately 60% in the absence of taking other preventative measures, which are costly. Reduced phosphorus contamination, as provided by the present invention, allows the catalyst to operate at high conversion efficiency over the life of the vehicle.
The inventors of the present invention have recognized that the effectiveness of the phosphorus trap is improved if it operates at a temperature close to the temperature of the catalytic converter. Thus, another advantage of the present invention is higher capture efficiency of deleterious phosphorus containing particles by placing the phosphorus trap in close proximity to the catalytic converter.
Another advantage of the present invention is that it removes particles of smaller diameter than prior approaches and does so with a neglible pressure drop across the phosphorus trap.
Yet another advantage of the present invention is that vehicles with unusual driving patterns may be operated in such a way to allow such vehicles to also benefit from the present invention.
The present invention may also be used to advantage combined with quick warmup strategies such as cold start spark retard and exhaust port oxidation.
The inventors of the present invention have recognized that the phosphorus trap may be much smaller than in prior approaches. The smaller size affects the warmup time of the exhaust system less than larger traps, a decided advantage in preventing cold start emissions.
Another advantage of the present invention is that, if the phosphorus trap is placed upstream of an exhaust gas oxygen sensor or other exhaust component sensor, deterioration of the sensor is prevented or slowed.
Without a phosphorus trap located upstream of a catalytic converter, the converter volume is chosen which provides sufficient conversion capacity over the targeted lifetime. An advantage of the present invention is that the volume can be reduced because the phosphorus trap protects the catalytic converter from phosphorus poisoning.
Yet another advantage is that, if the phosphorus trap is coated with a washcoat, it can provide some additional conversion capability, particularly during cold start.
The above advantages, other advantages, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.